How much will sea level rise?

… is the question people have been putting a lot of thought into since the IPCC AR4 report came out. We analysed what was in the report quite carefully at the time and pointed out that the allowance for dynamic ice sheet processes was very uncertain, and actually precluded setting a upper limit on what might be expected. The numbers that appeared in some headlines (up to 59 cm by 2100) did not take that uncertainty into account.

In a more recent paper, our own Stefan Rahmstorf used a simple regression model to suggest that sea level rise (SLR) could reach 0.5 to 1.4 meters above 1990 levels by 2100, but this did not consider individual processes like dynamic ice sheet changes, being only based on how global sea level has been linked to global warming over the past 120 years. As Stefan discussed, any non-linear or threshold behavior of ice sheets could lead to sea level rising faster than this estimate. Thus, otherwise quite conservative voices have been stressing the ‘unknown unknown’ nature of this problem and suggesting that, based on paleo-data (for instance), it was really hard to rule out sea level rises measured in feet, and not in inches. (Note too, the SLR is very much a lagging indicator, and will continue for centuries past the time that atmospheric temperatures have stabilised).

The first paper to really try and assess the future limits on dynamic ice sheet loss appeared in Science this week. Pfeffer et al looked at the exit glaciers for Greenland and West Antarctica and made some back of the envelope calculations of how quickly the ice sheets could dynamically drain.

Good news: they rule out more than 2 meters of sea level coming from Greenland alone in the next century. This is however more than anyone has ever suggested and would be comparable to the amount that disappeared at the Eemian (125,000 years ago) (see this post for more on that).

Bad news: they can’t rule out up to 2 meters in total.

In summary, they estimate that including dynamic ice sheet processes gives projected SLR at 2100 somewhere in the 80 cm to 2 meter range, and suggest that 80 cm should be the ‘default’ value. This is remarkable in a number of ways – first, these are the highest estimates of sea level rise by 2100 that has been published in the literature to date, and secondly, while they don’t take into account the full uncertainty in other aspects of sea level rise considered by IPCC, their numbers are significantly higher in any case. And this week the Dutch ‘Delta Commission‘ published its estimate of sea level rise that the Dutch need to plan for (p111): 55 to 110 cm globally and a bit more for Holland, based on a large number of scientists’ input. [Clarifying update: this is meant to be a “high end estimate”.]

Lest readers think this is no big deal, the estimates for the number of people who would be affected by 1 meter of sea level rise is more than 100 million – mainly in Asia. Of some recent relevance is the fact that the storm surge caused by Gustav in New Orleans was within 1 foot of the top of the levees. Another 3 ft caused by global sea level rise would have put a lot more water into the ‘bowl’.

Thus better estimates of sea level rise from ice sheets remain a high priority for the climate community. More sophisticated models and deeper understanding are coming along and hopefully those results will be out soon.

We were going to leave it at that, but we’ve just seen the initial media coverage where this result is being spun as a downgrading of predictions! (exemplified by this Reuters piece, drawing mainly from the U. Colorado press release). This is completely backwards. We stress that no-one (and we mean no-one) has published an informed estimate of more than 2 meters of sea level rise by 2100. Tellingly, the statement in the paper that suggests otherwise has no reference.

There have certainly been incorrect assertions and headlines implying that 20 ft of sea level by 2100 was expected, but they are mostly based on a confusion of a transient rise with the eventual sea level rise which might take hundreds to thousands of years. And before someone gets up to say Al Gore, we’ll point out preemptively that he made no prediction for 2100 or any other timescale. The nearest thing I can find is Jim Hansen who states that “it [is] almost inconceivable that BAU climate change would not yield a sea level change of the order of meters on the century timescale”. But that is neither a specific prediction for 2100, nor necessarily one that is out of line with the Pfeffer et al’s bounds.

Thus, this media reporting stands as a classic example of how scientists get caught up trying to counter supposed myths but end up perpetuating others, and miss an opportunity to actually educate the public. The problem is not that people think that we will get 6 meters of sea level rise this century, it’s that they don’t think there’ll be anything to speak of. Headlines like that in the Reuters piece (or National Geographic) are therefore doing a fundamental disservice to the public understanding of the problem.

Update: Marc Roberts sends along this cartoon illustrating the problem… (click for full size).

386 Responses to “How much will sea level rise?”

“The science is not yet done, and yet you are convinced that it can’t happen. Based on what? – gavin]”

It’s not the job of the skeptic to provide negative evidence. It’s up you your side to provide the evidence. You should already know that, that’s science 101. Hansen et al are throwing wild speculative numbers of how high sea level will go in the future. It’s their reponsibility to give a time frame. Not mine to show which time frame it cannot be.

[Response: Hansen et al have written many papers on just this issue, all of which are available on their website. They have given their reasoning at some length. Yet you are convinced they must be wrong based on a position of pure ignorance. If you were a real sceptic, you might open your mind to the possibility that your initial idea might in fact be wrong. I’ve been perfectly up front that there aren’t good estimates for the time scale and that paleo information only tells us that it has happened in centuries before and it has changed by meters before. And if something happened in the past, you clearly can’t say it is in principle impossible. – gavin]

Richard Wakefield — The last vestigaes of the Lauentide ice sheet in northern Canada melted away in the 1930s and 1940s, leaving only some ice caps on Ellsmere and Baffin Islands, Nunavut. So some AGW happened before 1980 CE.

I know of no paleodata which provides good constraints on further ice loss rates. This thread starts with discussing a paper which uses current observations to make a prediction for 2100 CE; looks reasonable.

However, it is not clear that the paper takes the closure of the ozone hole over Antarctica into account. This might well make some difference. Rather than carrying on, why don’t you see if somebody has already published regarding this anticipated event?

If the sea level is rising by 0.1m to 1.3m by 2100, that is a HUGE error bar.

It is still going UP.

Richard, #200 in what scenario? Do you think there is going to be ANY maths (we in the UK can do more than one sum, you know) that show that a warmer pole causes ice to freeze? If you are given a mathematical equation that, when all errors are put in, comes to “reduces by between 300,000sq mi and 1.3m sq mi”, what will you do? Keep complaining that you need better information or the errors don’t include EVERYTHING (and, when asked what is missing, just wave your hand and say “well, you can’t prove you’ve included everything, can you?”) and ask for better numbers.

It is, however, the job of the skeptic to actually listen to the answers he has solicited. If you can’t do that, and if you persist in irrelevant insults, such as “Boy you people really do not know the difference between speculation and hard science,” you are apt to find yourself ignored.

For systems which are highly nonlinear and driven far-from-equilibrium, such as ice sheets displaying endemic instability and structural morphogenesis, any maths that the human race writes down would be silly. The ice sheets have got the human race snookered in every respect.

What maths can be written down for the massive oceanic vortices that are erupting as the antarctic circulation destabilises leading to shock wave transmission and vortex grinding through the undersides of the ice sheets?

What maths can be written down for the seismic bursts sweeping across Antarctica which have now been detected?

What maths can be written down for the ice quakes that are ripping through the Greenland ice sheet? (Humans still seem to have a problem writing down maths that state when a particular earthquake will happen … let alone maths describing the insidious phenomenon being faced with GIS ice quakes).

What maths can be written down for the intermittent oceanic circulations as they falter?

What maths should be written down for coupled ice sheets as oceanic-mediated shock waves exchange between the SH and NH ice caps?

Which of Thom’s catastrophes should be chosen for any of these instabilities?

What maths can be written down for the increasing cascades of marine animals, some from the deepest parts of the oceans and never before seen, as they are swept to shore by the oceanic circulatory intermittencies and disintegrations?

What maths can be written down as ice shelves disintegrate? What maths can be written down for the dispersal of the Larsen B and increasing numbers of other ice shelves as they plop into the seas?

Mother Earth has done the maths, but the human race sure does not have the mental capacity to handle the shock and awe functionals, and multiplicities of nonlinearities, thesholds and singularities.

What is worth asking for is an element of insight and the ability to appreciate the perilous nature of what is unfolding. What is also worth asking for is humility.

It is not worth asking for the maths. Mother Earth will show a representation of it when she is ready.

Some glaciers and ice streams periodically lurch forward with sufficient force to generate emissions of elastic waves that are recorded on seismometers worldwide. Such glacial earthquakes on Greenland show a strong seasonality as well as a doubling of their rate of occurrence over the past 5 years. These temporal patterns suggest a link to the hydrological cycle and are indicative of a dynamic glacial response to changing climate conditions.

“The last vestigaes of the Lauentide ice sheet in northern Canada melted away in the 1930s and 1940s, leaving only some ice caps on Ellsmere and Baffin Islands, Nunavut. So some AGW happened before 1980 CE.” Prove it. Peer reviewed paper that supports that claim please.

Re 204:

“Very simple science says that CO2 causes global warming. Very simple science shows that a huge amount of CO2 now in the atmosphere is anthropogenic in origin.” But the interactions within the climate, the number of variables involved is not simple. That’s why millions are spent on super computer to try and model it. It’s not simple at all. If you think it is then that is why you are not skeptical of these wild alarmist claims made by the AGW community.

Re 205:

“If the sea level is rising by 0.1m to 1.3m by 2100, that is a HUGE error bar.

It is still going UP.” and has been for 12,000 years.

“Richard, #200 in what scenario? Do you think there is going to be ANY maths (we in the UK can do more than one sum, you know) that show that a warmer pole causes ice to freeze? If you are given a mathematical equation that, when all errors are put in, comes to “reduces by between 300,000sq mi and 1.3m sq mi”, what will you do? Keep complaining that you need better information or the errors don’t include EVERYTHING (and, when asked what is missing, just wave your hand and say “well, you can’t prove you’ve included everything, can you?”) and ask for better numbers.

So what do we get out of our efforts?”

Look, it should be simple to put a minimum on how fast the ice in Greenland can melt. Example. Assume that the area does not freeze at all for X number of years. How long would it take to melt all the ice? That’s the fastest it can possibly melt. Then you have to extend that time for every day it is colder that OC according to the IPCC worse case increase temp, then extend it for every snow fall that is less than loss. Then you will have a ball park range of years in the future it would take to melt all that ice. Then do the same thing for Antarctica. Someone must be able to do such a calculation. I suspect that it would take at least 1000 years. And since much can change in 1000 years it makes any meaningful prediction purely academic. But what it does do is end these wild prediction where the public thinks these worse case scenarios are imminent, not hundreds or even thousands of years away.

Imagine the impact Gore would have if he qualified his picture of New York submerged if he added the qualifier: “but this will take at least a thousand years to happen.” His alarmism would die immediately., and he would lose his message.

Re 206:

I AWAYS listen to all sides. I have YET to see anyone here answer my question. [edit]

On decommisioning nuclear plants that are presently at sea level: they actually have to be completely disassembled and removed to higher ground. The London Dumping Convention does not permit the disposal of nuclear waste at sea. So, the Humboldt Bay power plant, which has been decommissioned with the core parts stored on site, will have to be redecommisioned in the face of sea level rise.

The reason power plants are built at sea level is because there is plenty of cooling water there. Sea level rise is going to force some of these to close early driving up the cost of electricity as a result.

208. Mr Roberts, I read the Ekstrom paper when it came out so very long ago. Don’t cite such old work to me when challenging the words used to describe nonlinearities.

Please go away and find some uptodate cites to throw at me to challenge the descriptive words used for discontinuous and abrupt behaviours. Please go away and get a cite on the Richter-equivalence level of the ice quakes happening now on GIS. Once you have got those Richter-equivalence numbers, I suggest you make a list of the adjectives that you suggest might be appropriate to describe the abrupt dynamics.

The nature of discontinuities are such that they breed dramatic change. If you don’t like the words naturally appropriate to describe such abrupt things that’s tough.

Okay, as you’re not the geologist Wakefield of the same name, or JRWakefield (the Canadian software guy) — both frequent commentsrs in climate threads various places online. Are you any of the JR Wakefields who have long histories in climate discussions online?

If you’re brand new to this, people will, I think, cut you more slack if you make clear you’re not them.

Taking two of your questions, trying to be helpful here:
And
> Laurentide

You can look this up for yourself. For questions answerable by maps an image search is often useful:

> it should be simple to put a minimum on how fast the ice in Greenland can melt.

Frequently answered question. It depends.

!) the ice stays in place and melts slowly from the edges, top, and bottom (the old paradigm up to a few years ago) or
2) the ice breaks up and melts in pieces (see glacial earthquakes, outburst floods, water courses under ice caps, Lake Vostok, radar mapping and much else changing).

Gavin, reading your thoughts about Antarctica i can’t help but wonder.

‘Sea Level, Ice, and Greenhouses — FAQ ‘ at http://www.radix.net/~bobg/faqs/sea.level.faq.html indicates that there seem to exist a real possibility
” That West Antarctica can collapse much faster than Greenland relies on another oddity of the West Antarctic geometry. Most of the ice sheet base rests well below sea level (500 – 1000 meters below). The important oddity is that as you move further inward, the land is further below sea level. So, consider a point near the grounding line (the point on land where the ice shelf meets the ice sheet). Ice flows from the grounded part into the floating part.

The rate of flow increases as the slope (elevation difference) between the two sections increases. Extra mass loss in the ice shelf means that the shelf becomes thinner (and lower) so more ice flows in from the ice sheet. This makes the ice sheet just a little thinner. _But_ at the grounding line, the ice sheet had just enough mass to displace sufficient water to reach the sea floor. Without that mass, what used to be ice sheet begins to float. Since the sea floor slopes down inland of the grounding line, the area of ice sheet that turns into ice shelf increases rapidly. More ice shelf means more chance for ice to be melted by the ocean.

The collapse mechanism has a mirror-image advance mechanism. Should there be net accumulation, the ice sheet/shelf can ground out to the continental shelf edge. Go back to near the grounding point. This time add some excess mass to the ice sheet/shelf. This thickens the system to ground ice shelf. The grounded ice shelf takes area away from the ocean ablation zone, which makes the mass balance even more in favor of accumulation. So the advance can also be a self- accelerating
process. ”

As we, as I understand it, have found that there is an abundance of ‘ice-tunnels’ under the ice undermining the stability of the ice-sheet and accelerating its collapse why look at the surface. I know that this rapport from Robert Grumbine at bobg@radix.net is from -97 but its conclusions seems even more dangerous now considering those ” subglacial water system beneath the West Antarctic ice sheet (WAIS) ..who.. is causing scientists to rethink the mechanisms that control the flow of ice streams into the Ross Ice Shelf and ultimately into the Southern Ocean. ”

I have a distinct feeling that we have already passed our point of no return here. And the idea of a moratorium on all CO2 emissions won’t make a difference for us the nearest decades at least, considering that most scientists consider the cycle from CO2 being released until returning now to be at least a hundred years (?) if I got it right. And the ‘CO2 heat-sinks’ are getting saturated so what will take it up and ‘isolate’ it after those are ‘filled’?. What about the rising water temperatures in our oceans, and also, how will the rising acidity influence the deposits of methane under water?

If the frozen methane hydrate under water starts to release its methane it will make no difference if its cycle only is twelve years, right. It all hangs together as someone said. To me IPCC seems more about lifting forward the lowest common nominator than about ‘keeping to the middle’. So what are your thoughts on that?

I am no expert on this topic, but:
“Example. Assume that the area does not freeze at all for X number of years. How long would it take to melt all the ice? That’s the fastest it can possibly melt.”

This is clearly underestimating the complexity of the issue. “The area does not freeze” is not nearly enough information for predicting the time it will take. It will depend on the weather: how much wind, how much rain, what temperature do we have? And how will the ice sheet dynamics respond (in particular: what happens to the flow speed of the glaciers?). Those aren’t easy questions at all.

Richard Wakefield says: “Look, it should be simple to put a minimum on how fast the ice in Greenland can melt. Example. Assume that the area does not freeze at all for X number of years. How long would it take to melt all the ice? That’s the fastest it can possibly melt.”

Good Lord, Man. Do you realize the astounding ignorance in that statement? You do realize that ice melts very differently if you break it up so it has more surface area, don’t you? And that if you’ve got water running through crevasses, that it will speed up melt? And that if it slides into the Ocean, and calves into glaciers, it will melt faster. Sounds to me like another case of thinking anything you don’t understand must be easy.

Now think about this Richard. If you can be so astoundingly wrong about this, are you willing to maybe entertain the possibility that you could also be clueless about the climate as well? Think it might be worth considering?

“Thomas Lee Elifritz Says:
9 September 2008 at 10:52 PM
I have YET to see anyone here answer my question.

Have you ever considered doing your own research?”

If I had access to data and super computers I would.

“The heat capacities of the ocean and ice sheets are fairly straight forward, what is somewhat less than straightforward are the integrated forcings over time.

What is not misunderstood is the result of 2500 ppm atmospheric carbon dioxide. Clearly ALL of the ice will be gone in ‘on the order’ of roughly a millennium.”

What evidence do you have that we will reach 2500 ppm CO2? 450 ppm is projected in the future as a maximum is it not? So you are agreeing with me that it will be 1000 years. At 2500 ppm? If so then it will take much longer than 100 at the 450 wont it. Thus, do yu agree then that RC should call Hansen and Gore on the carpet for not giving a time fram and leaving misinformation in the mind of the public? Again, how much punch would Gore have if he had to admit that it would be a millennium at the earliest for New York to be under 25 feet of water?

“Also not misunderstood is the nonlinear evolution of the result, whether the timescale be 100 years or 1000 years.” So that is an excuse to not give it a try?

Look, people. This is real simple. You try a thought experiment first. This is done all the time in science as a starting point. Take the ice mass of Greenland and float it in the middle of the Pacific. How long would it take to melt? Then start adding real world parameters to the equations and see what effect this has on the duration of melting. What’s the problem people? This is science, not religion. Seems people here are trying to come up with any excuse NOT to find out. Or are you afraid of what the result may show?

“Okay, as you’re not the geologist Wakefield of the same name, or JRWakefield (the Canadian software guy)” That I am, you were not clear.

What is your point about the Laurentide? Gaven’s claim was: #192 “Collapsing ice sheets have lead to SLR of meters per century in the past (MWP 1A, or even the early Holocene final collapse of the Laurentide). We know that 4-6 meters of sea level are consistent with a further warming of the poles of 3 to 5 deg C (compare to the Eemian). Collapse of the WAIS is not a fiction. It has happened before. But though no-one can say how fast it happened,”

Bingo. First there is no way of knowing how high the average global temp will go over any time frame, hence there is no way of knowing how long it will take to melt Greenland.

Both of you are not following. Of course it’s complex. That why the radical predictions by Gore et al cannot be trusted! If it’s so complex how can they come up with ANY prediction at all?

[Response: They don’t. They do say that the uncertainties are very large – and uncertainties cut both ways. If you have no information, than you can’t rule anything out. We have some information and so we can. But not very satisfyingly. – gavin]

You are also missing the whole point of a thought experiment. You start simple and then proceed to add more and more complexity until you think you have a model of reality. That’s what climate models do. If you are claiming it is too complex to calculate then you are admitting defeat. You are also admitting that all of climate science is too complex and hence no predictions of any kind can be done.

No, don’t add any more heat than there is today. That’s unfair. Just today’s temp. Some icebergs last years in the oceans before completely melting, much smaller than Greenland.

Then start to change the numbers by dropping the temp (higher lattatude). Then add in some freezing time. Then add in more acculated snow fall.

[Response: You asked for how long it would take for Greenland to melt in the central Pacific, the first number indicates that there is plenty of energy to melt all of it. So the only determinant of the time scale is the surface area – Greenland diced into ice cubes would melt immediately. But this is nothing to do with anything. – gavin]

“In the most extreme scenario, using a carbon dioxide level of 1,000 ppm, the study predicts temperatures to rise by 8° Celsius (18° Fahrenheit) by the year 2050. This, in turn, would raise sea levels by 7 meters (23 feet) in a thousand years.”

[Response: Part of piece you didn’t quote: “We’re not saying how long it will take to get to the three degrees or how long it will take to lose the ice sheet,”. Note also the absence of a dynamic ice sheet response in the model they used, rendering all discussions of timescale rather problematic (as the authors themselves acknowledge). – gavin]

“Although current cumulative carbon dioxide emissions are on the order of 350 GtC, total emissions may reach 2,480 GtC by AD 2100 under worst-case scenarios — so unless emissions are curbed, runaway melting of Greenland may be triggered in the coming centuries.”

[Response: Yet another model with no ice sheet dynamical response: “this study probably underestimates the impact of the rapid dynamics of the Greenland ice sheet”. ]

“The Greenland ice sheet is all but doomed to melt away to nothing, according to a new modelling study. If it does melt, global sea levels will rise by seven metres, flooding most of the world’s coastal regions.

Jonathan Gregory, a climatologist at the University of Reading, UK, says global warming could start runaway melting on Greenland within 50 years, and it will “probably be irreversible this side of a new ice age”. The only good news is that it a total meltdown is likely to take at least 1000 years.”

[Response: Your point? All of Greenland didn’t disappear even at the Eemian. – gavin]

“The global warming doomsday writers claim the Greenland and Antarctic ice sheets are melting catastrophically, and will cause a sudden rise in sea level of 5 or more metres. This ignores the mechanism of glacier flow which is by creep. Glaciers are not melting from the surface down, nor are they sliding down an inclined plane lubricated by meltwater. The existence of ice over 3 km thick preserving details of past snowfall and atmospheres, used to decipher past temperature and CO2 levels, shows that the ice sheets have accumulated for hundreds of thousands of years without melting. Variations in melting around the edges of ice sheets are no indication that they are collapsing. Indeed ‘collapse’ is impossible.”

[Response: You are just erecting strawmen here. No one has claimed there will be a “sudden rise in sea level of 5 or more meters”, and the claim that the ice sheets haven’t melted in hundreds of thousands of years is only true for a complete melt. But they have lost meters of sea level over that time – including a collapse of the WAIS. So it isn’t impossible at all. And to claim that because a “sudden 5 m rise” is unlikely, that means there is no problem is just idiocy. – gavin]

Although the reply to #223 gave me a big laugh, on a general point surely there are more pressing implications from this subject than indulging (and rewarding) such breathtaking, relentless rude ignorance? I’d love a little bit of reflection on my #180, for example…

I’m still waiting for peer reviewed papers showing that 1850-1945 warming was due to human emitted co2.

Since there isn’t any, then the following logic is implied.

Rate of sea level has been within a narrow range averaging 1.7mm.yr for the past 110 years at least. This is observed from in situ measurements. The first 100 years was during a warming trend where humans were a very small contributor of CO2 emissions (14% of today’s).

Thus during the first 100 years of this warming trend we could not have been the contributors due to CO2 emissions. Thus the rate of sea level from that warming trend cannot be anthropic.

Since the rate of sea level rise in the last 70 years has not broken through the decadal variation, then the current sea level rise cannot be anthropic in spite of an 8 fold increase in CO2 emissions.

Breaking through the decadal variation is important. The current rate of 2.4-3.2mm/yr is within this variation, hence not an indicator of AGW. Not until it breaks through that variation can one make the claim that it is finally accelerating.

Richard, Do you understand the utter irrelevance and futility of ranting against the science on a blog whose whole purpose is to try to teach you about that science? Want to learn the science? Great, ask some relevant questions to fill in the blanks in your understanding in a respectful way.

Don’t like the science? Well, tough. Unless you want to go out and publish a whole bunch of papers in peer-reviewed journals that overturn the foundations of 150 years worth of climate science, you’re kind of stuck. See, try as they might–and they have really tried–climate scientists have not been able to come up with theories/models that explain the climate with a CO2 sensitivity less than 2 K/doubling. You are welcome to try, but without your own publication record showing it can be done, people who really know the field probably aren’t gonna take you seriously.

“[Response: Part of piece you didn’t quote: “We’re not saying how long it will take to get to the three degrees or how long it will take to lose the ice sheet,”. Note also the absence of a dynamic ice sheet response in the model they used, rendering all discussions of timescale rather problematic (as the authors themselves acknowledge). – gavin]”

EXACTLY!!! You just agreed with my position. Thus, again, to not include this caveat when giving predictions is irresponsible. So it could very well take thousands of years to all melt, or as you note “All of Greenland didn’t disappear even at the Eemian. – gavin]” So you now disagree, and will correct, anyone here who claims it will all melt and in short time, right? You will publicly claim to the MSM these uncertainanities right?

[Response: What are you arguing with? If all you wanted was a statement that all of Greenland is not likely to melt, then why didn’t you stop at the opening post paragraph 4? No-one has claimed all of Greenland will melt in a short time. – gavin]

“Part of the explanation for the inconsistency between palaeoclimate data and
IPCC projections lies in the fact that existing ice sheet models are missing
realistic (if any) representation of the physics of ice streams and icequakes,
processes that are needed to obtain realistic nonlinear behaviour. In the absence
of realistic models, it is better to rely on information from the Earth’s history. …

That history reveals large changes of sea level on century and shorter timescales.
All, or at least most, of glacial-to-interglacial sea-level rise is completed
during the ca 6 kyr quarter cycle of increasing insolation forcing as additional
portions of the ice sheet experience albedo flip. There is no evidence in the
accurately dated terminations (I and II) of multi-millennia lag in ice sheet
response.”

Hansen’s case is like the corpse of poisoned Pope at a Borgia family picnic. Something of an embarrassment all around. There’s nothing (outside the geological record) for scientists — who want to stir the world to action entirely with decorum and sobriety — to point to in their print outs and models. And yet there’s the stubborn geological record with its sub-millennial transitions. And, of course, there’s the awkward agreed-upon magnitude of the forcing from GHGs (much greater than orbital insolation changes).

Were I a scientist with Hansen’s understanding of all the physics and processes involved in these issues, it would probably take elephant tranquilizers to get me unconscious at night. This isn’t Area 51 stuff. Nobody seriously disagrees with the speed with which glaciation terminates. Nobody seriously pegs the forcing due to changes in insolation as more than a fraction of the forcing due to GHGs. Which is where my dead-Pope-at-the-Borgia’s image comes from. It would be impolite and impolitic to suddenly grab people by the lapel and scream, but apparently we’re really going to need a trickle of water at our feet to get moving.

Changes in the climate system’s energy budget are predominantly revealed in ocean temperatures and the associated thermal expansion contribution to sea-level rise. Climate models, however, do not reproduce the large decadal variability in globally averaged ocean heat content inferred from the sparse observational database, even when volcanic and other variable climate forcings are included. The sum of the observed contributions has also not adequately explained the overall multi-decadal rise. Here we report improved estimates of near-global ocean heat content and thermal expansion for the upper 300 m and 700 m of the ocean for 1950–2003, using statistical techniques that allow for sparse data coverage and applying recent corrections to reduce systematic biases in the most common ocean temperature observations. Our ocean warming and thermal expansion trends for 1961–2003 are about 50 per cent larger than earlier estimates but about 40 per cent smaller for 1993–2003, which is consistent with the recognition that previously estimated rates for the 1990s had a positive bias as a result of instrumental errors. On average, the decadal variability of the climate models with volcanic forcing now agrees approximately with the observations, but the modelled multi-decadal trends are smaller than observed. We add our observational estimate of upper-ocean thermal expansion to other contributions to sea-level rise and find that the sum of contributions from 1961 to 2003 is about 1.5 ± 0.4 mm yr-1, in good agreement with our updated estimate of near-global mean sea-level rise (using techniques established in earlier studies) of 1.6 ± 0.2 mm yr-1.

Gavin, where does it say in this paper that the cause of sea level rise is due to AGW?

[Response: You’re right, ocean warming must be due to some other mysterious energy force that is causing the planet to be out of energy equilibrium. – gavin]

“[Response: What are you arguing with? If all you wanted was a statement that all of Greenland is not likely to melt, then why didn’t you stop at the opening post paragraph 4? No-one has claimed all of Greenland will melt in a short time. – gavin]”

Gore does it implicitly by showing a modern New York getting swallowed by 25 feet of sea and says it’s from Greenland melting. Greenpeace does it which is why they are being sued in Spain. You are missing my point.

You are agreeing with me that this cannot happen in less than 1000 years. Even agreeing it is unlikely to all melt at all.

So we come back to the main question. When are you going to publicly tell the MSM this and ask Gore to include this caveat in his presentations?

[Response: Gore stated correctly that if Greenland melts it will cause sea level to rise 6 meters. I would have been happier if he said that the timescale for such a thing is likely long but uncertain. But I have no confidence that the timescale is 1000 years, and I have no confidence that this implies that sea level rises of 1 meter or more can’t happen in a century. Greenland is not the only ice sheet remember and all of the estimates you quoted did not include dynamic ice processes. Both Gore and the MSM read this blog, but everything here was stated in the opening post already. – gavin]

Richard Wakefield (223) wrote “If I had access to data and super computers I would [do my own research].” There are plenty of accessible papers to read and ice core data, for example, is easily available; a super-computer is not required, although internet access is highly desirable.

From the NOAA Paleoclimatology web site one can obtain, for example, the Petit et al. Vostok temperatures for the Eemian. From this one sees that the temperatures there where above recent temperatures for over 4,800 years; during this interval, the Greenland ice sheet partially melted away, there being a graphic of the result reproduced in IPCC AR4.

you can compute the equilibrium warming due to additional CO2 for any period for which CO2 concentrations are available. For example, from 1750 CE to 1850 CE, anthropogenic CO2 contributed 0.08 K (equilibrium) warming to whatever the actual temperture cahnge was. Now correct this for the very fast (less than 7 years) warming, about 60% of the equilibrium to obtain 0.05 K, about half the effect of the change in TSI over a typical sunspot cycle.

Dear Mr Wakefield, why should I trust your gut feelings about how fast the Greenland ice will melt. You give me no reason to believe you know the first thing about these matters.

For your information, the main method by which an ice sheet melts is not due to solar energy, which will not change in Greenland over the next century, but due to the transfer of latent heat from water vapour. Ben Nevis in Scotland, roughly the same height as the Greenland ice sheet receives 4 m (12 feet) of precipitation per year. The latent heat of ice is 333 J/g, the latent heat of water vapour is 2,500 J/g. That means that there is enough latent heat released above Ben Nevis by condensation to melt 30 m (100 feet) of ice each year. In one hundred years 3 km of ice would melt, which is about the average depth of the Greenland ice sheet.

When the Arctic sea ice disappears, there will be an additional source of water vapour to melt the Greenland ice. And as the ice melts its upper surface will sink to lower and warmer altitudes. It is just feasible that the Greenland Ice could be gone this century :-(

Re Hank @ 215: “Okay, as you’re not the geologist Wakefield of the same name, or JRWakefield (the Canadian software guy) — both frequent commentsrs in climate threads various places online…”

Hank, he is indeed the Canadian software guy (see his reply @ 224) from Kamoka, a suburb of London, Ontario, and he is anything but brand new at this, “this” meaning infesting and disrupting global warming/climate change threads with his pompous and ludicrous hand waving and windmill tilting.

Since it now seems clear that Richard Wakefield doesn’t actually want to do any research, I’m looking for a volunteer to go to the NOAA Paleioclimatology web site, acquire the NGISP (northern Greenland) temperatures and determine the length of the Eemian interglacial, here defined as from the year the temperature first rose to that of the local 1850 CE temperature until it once again falls below that temperature. That will provide a good estimate for the time interval required, under those prevaling conditions, for the Greenland ice sheet to raise the sea level its share of the 4–6 observed meters. (Surely WAIS contributed ssome as well.)

“you can compute the equilibrium warming due to additional CO2 for any period for which CO2 concentrations are available. For example, from 1750 CE to 1850 CE, anthropogenic CO2 contributed 0.08 K (equilibrium) warming to whatever the actual temperture cahnge was. Now correct this for the very fast (less than 7 years) warming, about 60% of the equilibrium to obtain 0.05 K, about half the effect of the change in TSI over a typical sunspot cycle.”

So in other words no meaurable effect at all. Problem is, we cannot rewind the clock and take our CO2 out and see what happens can we. Thus I maintain, 1850-1945 CO2 emissions had virtually NO effect on the temperature. It would have risen anyway. Hence my logic example stands. The current rate of sea level, 1.7mm/yr over the last 110 years, cannot be from AGW. The current decadal measurement is due to varations, that even the paper Gavin suggested, shows is just normal variation.

“Dear Mr Wakefield, why should I trust your gut feelings about how fast the Greenland ice will melt. You give me no reason to believe you know the first thing about these matters…. It is just feasible that the Greenland Ice could be gone this century.”

Not according to Pfeffer et al. They give an upper limit. That’s what this is all about. So your dire predictions are not agreed with by the peer reviewed papers.

And that 1000 year is not from me, don’t even try to shoot the messenger (common dogmatist tactic), go after the people who published the papers I quoted. That’s how science works. Publish in a peer reviewed paper showing why they are wrong and you are right. Until then, what you present is nothing but faith based suppositions.

It has been amusing at times to watch Richard Wakefield tie himself in knots trying to undermine AGW. But frankly it is troubling to think of the amount of time that Gavin and other scientists have wasted on this guy. I suppose it is necessary to refute nonsense when it is presented as science, but there is nothing you can say that will change Wakefield one iota. He is a troll, and he has dominated the discussion long enough.

I couldn’t agree more with #247. Real Climate is a place for serious discussion, not for denialists trolling whose response to logic and science is simply to shout louder and with seeming ever-greater arrogance and ignorance. This is starting to look like any other random, unmoderated internet forum.

Again, the wider issues are being ignored, and the consequences could not be more serious. Again I ask – what is the most appropriate response by other climate scientists to Hansen’s contention that SLR is very soon (months) to pass a tipping point where it cannot be stopped – however long that eventual process takes? While Hansen engages the world’s leaders on the issue, is it right that he does this (seemingly) alone?

“Gore does it implicitly by showing a modern New York getting swallowed by 25 feet of sea and says it’s from Greenland melting. Greenpeace does it which is why they are being sued in Spain. You are missing my point.”

Nope, he didn’t put any timeline on it and given how slow change in NYC happens in construction, why would it change much over a century? And if greenland can melt in five years based on the extra heating at that lattitude, it could be true.

Your “point” is wrong too because you have considered it only a thousand years for greenland ice sheet to melt. But answers given to you show this is unlikely.

Will NYC change in 5-10 years so much that you could tell it wasn’t todays NYC? No. Your refutation is wrong.